This application is based on applications Nos. 2000-51447 and 2000-80191 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an apparatus for and method of printing on a three-dimensional object.
2. Description of the Background Art
A printing apparatus which ejects ink onto printing paper by an ink jet technique to print a desired image and the like is conventionally known. In such a printing apparatus, an ejection head expels ink while continuously moving in a main scanning direction. Upon completion of printing of one line in the main scanning direction, the ejection head is moved a fixed distance in a sub-scanning direction orthogonal to the main scanning direction, and starts the next printing operation in the main scanning direction.
An attempt has been made to print on a three-dimensional object by using the technique of ejecting ink such as the ink jet technique.
However, printing by ejecting droplets of ink from the ejection head onto the three-dimensional object has a problem such that the density of dots changes with the surface shape of the object. More specifically, printing on a portion of the object which has a near-horizontal surface, like the printing on a surface of printing paper and the like, provides a high-density dot distribution, whereas printing on an inclined surface of the object results in a dot distribution which is sparse depending on the angle of inclination of the inclined surface.
FIGS. 36A and 36B show a conventional printing method for illustration of the above-mentioned phenomenon. FIG. 36A shows a dot distribution when printed on a horizontal surface, and FIG. 36B shows a dot distribution when printed on an inclined surface. For printing on a three-dimensional object, a conventional printing apparatus moves the ejection head stepwise every fixed distance in the sub-scanning direction, independently of whether a to-be-printed portion of the object has a horizontal surface or an inclined surface. The fixed distance is set at a distance d which provides a dense distribution of dots printed on the horizontal surface, as shown in FIG. 36A. Thus, when the to-be-printed portion of the object has an inclined surface at an inclination angle xcex8 with respect to the sub-scanning direction, the movement of the fixed distance d of the ejection head in the sub-scanning direction as shown in FIG. 36B causes a dot-to-dot spacing on the inclined surface to equal d/cos xcex8, resulting in a sparse dot distribution.
This phenomenon also occurs in the main scanning direction in which the ejection head continuously moves. However, the problem of the above-mentioned phenomenon in the main scanning direction in which the ejection head continuously moves is relatively easily overcome by controlling the timing of ejection of ink from the ejection head or otherwise.
On the other hand, since the ejection head is driven stepwise in the sub-scanning direction after the continuous printing in the main scanning direction, the problem of the above-mentioned phenomenon in the sub-scanning direction is not overcome by merely controlling the timing of ink ejection.
To solve the above-mentioned problem in the case where the object is inclined with respect to the sub-scanning direction, it is contemplated to incline the ejection head in accordance with the inclined surface so that the ink is always ejected in a direction normal to the inclined surface to perform sub-scanning through the fixed distance d along the inclined surface. Such an arrangement, however, increases the complexity of driving mechanisms and operational control, and accordingly increases the size of the apparatus.
For a printing apparatus for printing on a two-dimensional object (e.g., printing paper), there has been no need to consider the surface shape of the object which is constant or flat. However, for printing on the three-dimensional object, it is necessary to consider the three-dimensional shape of the object to achieve proper printing.
In many of the printing apparatuses for printing on the two-dimensional object (e.g., printing paper), a slight positional deviation of the printing paper does not become a problem. However, for printing on the three-dimensional object, a positional deviation of the object results in improper printing. For example, when applying different colors to two adjacent faces bordered by an edge, there is a problem such that a deviation of the coloring position is very conspicuous to result in remarkable deterioration of a print quality.
Thus, the printing on a three-dimensional object is required to take the three-dimensional shape of the object into consideration to provide a high print quality.
The present invention is intended for an apparatus for providing ink to a surface of a three-dimensional object. According to a first aspect of the present invention, the apparatus comprises: a shape recognition section for obtaining data about a surface shape of a three-dimensional object; an ejection section for ejecting ink toward the three-dimensional object; a scanning section for causing the ejection section to scan relative to the three-dimensional object; and a control section for controlling an operation of the ejection section and/or the scanning section in accordance with information about inclination of the surface of the three-dimensional object, the information being indicated in the data obtained by the shape recognition section.
Thus, the operation of the ejection section and/or the scanning section is controlled in accordance with the information about the surface inclination of the three-dimensional object, the information being indicated in the data obtained by the shape recognition section. Therefore, the apparatus can perform a high-quality printing process.
According to a second aspect of the present invention, in the apparatus of the first aspect, the scanning section performs a plurality of continuous main scanning operations in a predetermined operations, and repeats a sub-scanning operation for each of the continuous main scanning direction. The operation of the scanning section controlled by the control section is the sub-scanning operation.
Thus, the operation of the scanning section controlled by the control section is the sub-scanning operation. Therefore, the apparatus can provide a uniform distribution of dots of ink in the sub-scanning direction when printing on the three-dimensional object.
According to a third aspect of the present invention, in the apparatus of the first aspect, the ejection section comprises a plurality of nozzles for ejecting ink, and the operation of the ejection section controlled by the control section is to make a predetermined one of the plurality of nozzles available or unavailable.
Thus, the predetermined one of the plurality of nozzles is made available or unavailable. Therefore, the apparatus can eject ink within tolerance of a target position on the object.
According to a fourth aspect of the present invention, in the apparatus of the first aspect, the shape recognition section comprises a sensor for measuring the surface shape of the three-dimensional object to obtain the data about the surface shape of the three-dimensional object. The sensor is caused to scan the surface of the three-dimensional object along with the ejection section by the scanning section in order to determine the height of a predetermined point on the surface of the three-dimensional object with respect to a predetermined reference plane.
Thus, the shape recognition section comprises the sensor for measuring the surface shape of the three-dimensional object to obtain the data about the surface shape of the three-dimensional object. The sensor is caused to scan the surface of the three-dimensional object along with the ejection section by the scanning section in order to determine the height of the predetermined point on the surface of the three-dimensional object with respect to the predetermined reference plane. Therefore, the apparatus can efficiently obtain the data about the surface shape of the three-dimensional object.
According to a fifth aspect of the present invention, the control section moves the ejection section stepwise every fine pitch in the sub-scanning direction, and controls the main scanning section to effect main scanning at a position at which the amount of movement of the ejection section in the sub-scanning direction equals a travel pitch.
Thus, the control section moves the scanning section stepwise every fine pitch in the sub-scanning direction, and controls the main scanning section to effect main scanning at the position at which the amount of movement of the ejection section in the sub-scanning direction equals the travel pitch. This achieves efficient printing.
It is an object of the present invention to provide an apparatus for and method of printing which can print on a three-dimensional object with high quality.
It is another object of the present invention to provide an apparatus for and method of printing which can constantly provide a uniform distribution of dots of ink particularly when printing on a three-dimensional object.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.